Air Pollution in The Upper Troposphere: Insights from In-Situ Airplane Measurements (1991–2018)

Abstract. Long-lived atmospheric species like carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and CFCs exhibit discernible trends reflecting anthropogenic emissions, with increases observed in CO₂, CH₄, N₂O, and decreases in CFCs. Conversely, trends for short-lived species like carbon monoxide (CO) and nitrogen oxides (NOx) remain less understood due to rapid chemistry and limited upper tropospheric observations. We utilize extensive in-situ CO measurements spanning 2012–2023, supplemented by prior airplane campaigns from 1991–2019, to examine short-term fluctuations in CO influenced by anthropogenic emissions and rapid chemical removal. Comparisons with MOPITT satellite data and chemistry budgets from 1948–2003 simulations further elucidate the interplay of sources and sinks, revealing the significant impact of chemistry on CO profiles and trends.